Fix up some loose ends for CURRENT_USER as RoleSpec

In commit 31eae602, some documents were not updated to show the new
capability; fix that.  Also, the error message you get when CURRENT_USER
and SESSION_USER are used in a context that doesn't accept them could be
clearer about it being a problem only in those contexts; so add the
word "here".

Author: Kyotaro HORIGUCHI

His patch submission also included changes to GRANT/REVOKE, but those
seemed more controversial, so I left them out.  We can reconsider these
changes later.

doc/src/sgml/ref/alter_policy.sgml

@@ -23,7 +23,7 @@ PostgreSQL documentation
 <synopsis>
 ALTER POLICY <replaceable class="parameter">name</replaceable> ON <replaceable class="parameter">table_name</replaceable>
     [ RENAME TO <replaceable class="PARAMETER">new_name</replaceable> ]
-    [ TO { <replaceable class="parameter">role_name</replaceable> | PUBLIC } [, ...] ]
+    [ TO { <replaceable class="parameter">role_name</replaceable> | PUBLIC | CURRENT_USER | SESSION_USER } [, ...] ]
     [ USING ( <replaceable class="parameter">using_expression</replaceable> ) ]
     [ WITH CHECK ( <replaceable class="parameter">check_expression</replaceable> ) ]
 </synopsis>

doc/src/sgml/ref/create_policy.sgml

@@ -23,7 +23,7 @@ PostgreSQL documentation
 <synopsis>
 CREATE POLICY <replaceable class="parameter">name</replaceable> ON <replaceable class="parameter">table_name</replaceable>
     [ FOR { ALL | SELECT | INSERT | UPDATE | DELETE } ]
-    [ TO { <replaceable class="parameter">role_name</replaceable> | PUBLIC } [, ...] ]
+    [ TO { <replaceable class="parameter">role_name</replaceable> | PUBLIC | CURRENT_USER | SESSION_USER } [, ...] ]
     [ USING ( <replaceable class="parameter">using_expression</replaceable> ) ]
     [ WITH CHECK ( <replaceable class="parameter">check_expression</replaceable> ) ]
 </synopsis>

doc/src/sgml/ref/create_tablespace.sgml

@@ -22,7 +22,7 @@ PostgreSQL documentation
  <refsynopsisdiv>
 <synopsis>
 CREATE TABLESPACE <replaceable class="parameter">tablespace_name</replaceable>
-    [ OWNER <replaceable class="parameter">user_name</replaceable> ]
+    [ OWNER { <replaceable>new_owner</replaceable> | CURRENT_USER | SESSION_USER } ]
     LOCATION '<replaceable class="parameter">directory</replaceable>'
     [ WITH ( <replaceable class="PARAMETER">tablespace_option</replaceable> = <replaceable class="PARAMETER">value</replaceable> [, ... ] ) ]
 </synopsis>

doc/src/sgml/ref/drop_owned.sgml

@@ -21,7 +21,7 @@ PostgreSQL documentation
 
  <refsynopsisdiv>
 <synopsis>
-DROP OWNED BY <replaceable class="PARAMETER">name</replaceable> [, ...] [ CASCADE | RESTRICT ]
+DROP OWNED BY { <replaceable class="PARAMETER">name</replaceable> | CURRENT_USER | SESSION_USER } [, ...] [ CASCADE | RESTRICT ]
 </synopsis>
  </refsynopsisdiv>
 

doc/src/sgml/ref/reassign_owned.sgml

@@ -21,7 +21,8 @@ PostgreSQL documentation
 
  <refsynopsisdiv>
 <synopsis>
-REASSIGN OWNED BY <replaceable class="PARAMETER">old_role</replaceable> [, ...] TO <replaceable class="PARAMETER">new_role</replaceable>
+REASSIGN OWNED BY { <replaceable class="PARAMETER">old_role</replaceable> | CURRENT_USER | SESSION_USER } [, ...]
+               TO { <replaceable class="PARAMETER">new_role</replaceable> | CURRENT_USER | SESSION_USER }
 </synopsis>
  </refsynopsisdiv>
 

src/backend/parser/gram.y

@@ -13216,13 +13216,13 @@ RoleId:		RoleSpec
 						case ROLESPEC_SESSION_USER:
 							ereport(ERROR,
 									(errcode(ERRCODE_RESERVED_NAME),
-									 errmsg("%s cannot be used as a role name",
+									 errmsg("%s cannot be used as a role name here",
 											"SESSION_USER"),
 									 parser_errposition(@1)));
 						case ROLESPEC_CURRENT_USER:
 							ereport(ERROR,
 									(errcode(ERRCODE_RESERVED_NAME),
-									 errmsg("%s cannot be used as a role name",
+									 errmsg("%s cannot be used as a role name here",
 											"CURRENT_USER"),
 									 parser_errposition(@1)));
 					}

src/test/regress/expected/rolenames.out

@@ -43,7 +43,7 @@ CREATE ROLE "current_user";
 CREATE ROLE "session_user";
 CREATE ROLE "user";
 CREATE ROLE current_user; -- error
-ERROR:  CURRENT_USER cannot be used as a role name
+ERROR:  CURRENT_USER cannot be used as a role name here
 LINE 1: CREATE ROLE current_user;
                     ^
 CREATE ROLE current_role; -- error
@@ -51,7 +51,7 @@ ERROR:  syntax error at or near "current_role"
 LINE 1: CREATE ROLE current_role;
                     ^
 CREATE ROLE session_user; -- error
-ERROR:  SESSION_USER cannot be used as a role name
+ERROR:  SESSION_USER cannot be used as a role name here
 LINE 1: CREATE ROLE session_user;
                     ^
 CREATE ROLE user; -- error